Various different back flow valves have been proposed for use in flow lines, as evidenced by the following U.S. Pat. Nos.: 4,201,626 to Asdigian; 526,649 to Hallock; 780,786 to Dunham; 3,302,688 to Thrush; 2,330,468 to Brisbane, et al; 1,461,439 to Burgin; and 3,911,502 to Boretos.
However, the above prior art is not always satisfactory for use in a meter run, because of the expense or because the complicated nature of the valve. It would be desirable to have made available an inexpensive back flow valve having a minimum number of parts, and which positively gravitates back into seated position whenever back flow occurs. It would furthermore be desirable if such a valve could be interposed between confronting flange faces, thereby enabling the valve device to be used upstream or downstream of a meter run by utilizing the existing meter run flanges.
Apparatus which achieves the above desired goal and at the same time overcomes the objections of the prior art is the subject of the present invention.